Field of the Invention
The invention is related to the field of graft copolymers. Provided are macromonomers, graft copolymers made from macromonomers, moisture barrier films, and articles formed therefrom. Also provided are processes for the synthesis of graft copolymers, and monomers used in said processes.
Description of the Related Art
A wide variety of thermoplastic polymers and films formed from such thermoplastic polymers are known. Important physical characteristics of such films include barrier properties, such as barriers to gas, aroma, and moisture, toughness, such as wear and weathering resistances, and light-transmittance. These properties are especially important in film applications, including use as packaging material for food or medical products.
Demand for flexible packaging materials with high moisture and oxygen barrier properties is constantly growing due to the advent of new drugs and drug-coated diagnostic devices. Conventionally, it has been desirable to use or incorporate fluoropolymer films in packaging applications, as they are known for their barrier properties, inertness to most chemicals, resistance to high temperatures, and low coefficients of friction. See, for example, U.S. Pat. Nos. 4,146,521; 4,659,625; 4,677,017; 5,139,878; 5,855,977; 6,096,428; 6,138,830; and 6,197,393, which teach multilayer fluoropolymer-containing films. Films including polychlorotrifluoroethylene (“PCTFE”) homopolymer or copolymers are particularly advantageous due to their excellent moisture barrier properties. Such films also exhibit high thermal stability, excellent toughness, and clarity at room temperature.
As fluoropolymer performance demands have increased, there has been a particular focus in the art on the relationship between fluoropolymer architecture and fluoropolymer properties. The study of structured fluoropolymers, such as fluorotelomers, fluorotelechelics, alternated copolymers, block copolymers, gradient copolymers, graft copolymers, and dendrimers has found that fluoropolymer properties may be directly affected by polymer architecture. With particular regard to graft polymerization, it is known that the properties of a fluoropolymer may be modified by grafting co-monomer pendant chains onto the fluoropolymer backbone. Depending on the nature of the co-monomers, these graft copolymers often retain the desirable properties of the parent fluoropolymer “backbone” while adding the desirable properties of the co-monomer pendent chains. See, for example, U.S. Pat. No. 4,308,359, which teaches polyvinylidenefluoride (PVDF) graft copolymers formed with ethylenically unsaturated co-monomers, such as a vinyl monomer, acrylonitrile, styrene, or an olefin. These graft copolymers have certain physical characteristics, such as better solvent resistance, workability, and adhesiveness than were previously known. U.S. Pat. No. 4,910,258 teaches fluorine-containing graft copolymers having a fluorine-containing elastomer copolymer backbone, for example a copolymer of vinylidene fluoride, chlorotrifluoroethylene (CTFE) and t-butyl peroxyallylcarbonate, and fluorine-containing crystalline polymer branches, for example copolymers of CTFE and ethylene. These graft copolymers are useful as a fluororesin intermediate between fluororubbers and crystalline fluororesins.
U.S. patent application publication 2007/0244262 teaches graft copolymers having a crystalline backbone such as poly(vinylidene fluoride-co-chlorotrifluoroethylene), poly(ethylene-co-chlorotrifluoroethylene), copolymers of chlorotrifluoroethylene with alkyl vinyl ether or alkyl vinyl ester, and poly(chlorotrifluoroethylene-co-vinylidene fluoride-co-tetrafluoroethylene), having amorphous side chains grafted thereto, such as polystyrene, poly(acrylic acid), or poly(tert-butyl acrylate). U.S. patent application publication 2007/0244262 specifically teaches away from graft copolymers having a PCTFE backbone due to the insolubility of PCTFE in the solvents required by their polymerization process.
As demand has grown, it has been met mainly by enhancing existing products. For example, PCTFE films are now available up to 150 μm thick, more than doubling their barrier properties relative to traditional 50 μm structures. However, while these thicker materials may meet the desired barrier properties, they are not cost effective and their use is restricted to specialty packaging applications. Such thicker films are also difficult to process as packaging films. One suitable way to reduce the cost of a packaging material fabricated from a costly polymer is to form multilayer structures in which the polymer film is laminated with other, less costly polymer films. However, fluoropolymers do not adhere strongly to most other polymers. In fact, most fluoropolymers are known for their non-stick characteristics. This is very disadvantageous, because poor bond strength between layers can result in the delamination of multilayer films. As a result, specialized intermediate adhesive layers that increase the cost of the packing structure are generally needed to attach most other polymer films to fluoropolymer films.
As such, there remains a need in the art for cost effective packaging films having improved moisture and oxygen barrier properties that meet present and future performance demands.